Noninvasive and Contactless Characterization of Electronic Properties at the Semiconductor/Dielectric Interface Using Optical Second-Harmonic Generation

Optical second-harmonic generation (SHG) is a reliable technique for probing material surface and interface characteristics. Here, we have demonstrated a non-destructive, contactless SHG-based semiconductor/dielectric interface characterization method to measure the conduction band offset and quantitatively evaluate charge densities at the interface in oxide and at the oxide surface. This technique extracts the interface-trapped charge type (donor/acceptor) and qualitatively analyzes the process-induced variation in interface states (Dit), oxide, and oxide surface state density. These qualitative and quantitative analyses provide us with a glimpse into the band bending. The metrology method is validated through a detailed characterization of the Si/HfO2 interface. An optical setup has been developed to monitor the time-dependent second-harmonic generation (TDSHG) from the semiconductor/oxide interface. The temporal characteristics of TDSHG are explained with its relationship to the filling of Dit and spatio-temporal trapping of photoexcited charge in oxide and at the oxide surface. A numerical solver, based on plausible carrier dynamics, is used to model the experimental data and to extract the electronic properties at the Si/HfO2 interface.

Preparation of Remote Plasma Atomic Layer-Deposited HfO2 Thin Films with High Charge Trapping Densities and Their Application in Nonvolatile Memory Devices

Optimization of equipment structure and process conditions is essential to obtain thin films with the required properties, such as film thickness, trapped charge density, leakage current, and memory characteristics, that ensure reliability of the corresponding device. In this study, we fabricated metal-insulator-semiconductor (MIS) structure capacitors using HfO₂ thin films separately deposited by remote plasma (RP) atomic layer deposition (ALD) and direct-plasma (DP) ALD and determined the optimal process temperature by measuring the leakage current and breakdown strength as functions of process temperature. Additionally, we analyzed the effects of the plasma application method on the charge trapping properties of HfO₂ thin films and properties of the interface between Si and HfO₂. Subsequently, we synthesized charge-trapping memory (CTM) devices utilizing the deposited thin films as charge-trapping layers (CTLs) and evaluated their memory properties. The results indicated excellent memory window characteristics of the RP-HfO₂ MIS capacitors compared to those of the DP-HfO₂ MIS capacitors. Moreover, the memory characteristics of the RP-HfO₂ CTM devices were outstanding as compared to those of the DP-HfO₂ CTM devices. In conclusion, the methodology proposed herein can be useful for future implementations of multiple levels of charge-storage nonvolatile memories or synaptic devices that require many states.

Band-Bending of Ga-Polar GaN Interfaced with Al2O3 through Ultraviolet/Ozone Treatment

Understanding the band bending at the interface of GaN/dielectric under different surface treatment conditions is critically important for device design, device performance, and device reliability. The effects of ultraviolet/ozone (UV/O₃) treatment of the GaN surface on the energy band bending of atomic-layer-deposition (ALD) Al₂O₃ coated Ga-polar GaN were studied. The UV/O₃ treatment and post-ALD anneal can be used to effectively vary the band bending, the valence band offset, conduction band offset, and the interface dipole at the Al₂O₃/GaN interfaces. The UV/O₃ treatment increases the surface energy of the Ga-polar GaN, improves the uniformity of Al₂O₃ deposition, and changes the amount of trapped charges in the ALD layer. The positively charged surface states formed by the UV/O₃ treatment-induced surface factors externally screen the effect of polarization charges in the GaN, in effect, determining the eventual energy band bending at the Al₂O₃/GaN interfaces. An optimal UV/O₃ treatment condition also exists for realizing the "best" interface conditions. The study of UV/O₃ treatment effect on the band alignments at the dielectric/III-nitride interfaces will be valuable for applications of transistors, light-emitting diodes, and photovoltaics.